The present invention generally relates to an improvement in a fluorescent lamp arrangement used as a back-light for a liquid crystal display (L.C.D.) panel, or the like, and particularly to a construction of a fluorescent lamp arrangement used as a back-light which can evenly and uniformly illuminate a liquid crystal display surface.
A conventional liquid crystal display has been arranged such that, as disclosed in Japanese Patent Unexamined Publication JP-A-48-47294 (1973), an elongated fluorescent lamp is provided at the back of a liquid crystal display panel and a reflector is attached behind the lamp. In this case, however, no consideration is given to the problem of uneveness of luminance on the surface of the liquid crystal display panel, so that luminance becomes extremely large at its portion just above the lmap and it cannot achieve uniformity of luminance over the whole surface. As disclosed in Japanese Patent Unexamined Publications JP-A-55-15126 (1980) and JP-A-55-133008 (1980), in order to decrease the quantity of light at a portion just above the light source, an arrangement has been proposed in which a transparent film having a reflecting material printed thereon is disposed horizontally between a diffusion board and the light source. In this arrangement, there is an effect of a decrease in unevenness in distribution of luminance when viewed in a direction perpendicular to the diffusion board. However, in the case where such transparent film is utilized in a liquid crystal display, or the like, it is difficult to satisfy the requirement such that the transparent film having the reflecting material would be effective to make the luminance uniform in any direction within a range of .+-.45 angular degrees with respect to the vertical direction, because the light source is viewed directly through the diffusion board when viewed obliquely beyond a certain angle smaller than 45 angular degrees with respect to the vertical direction, resulting in undesired visual angular characteristic.
There is another proposal in which, as disclosed in Japanese Patent Unexamined Publication JP-A-59-226303 (1984), a light source such as a light emitting diode (LED), an incandescent lamp, a tungsten halogen lamp or a fluorescent lamp is used in combination with a light diffusion plate made of transparent acryl material so as to obtain an area source of light illuminating above the transparent acryl plate. In this arrangement, however, the luminance is so small to be at most several hundreds nt (Cd/m.sup.2) which is insufficient to satisfy the requirements of obtaining luminance of 1000 nt or more for use in a liquid crystal TV receiver using color liquid crystal or the like and of reducing electric power consumption as much as possible.